Construction of maps from photographs taken from the air



7 Aug. 2, 1938 H. G. FOURCADE v 2,125,553

CONSTRUCTION OF MAPS FROM PHOTOGRAPHS TAKEN FROM THE AIR Filed April 12, 1937 2 Sheets-Sheet 1 Aug. 2, 1938. H. s. FOURCADE 2,125,553

CONSTRUCTION OF MAPS FROM PHOTOGRAPHS TAKEN FROM THE AIR Filed April 12, 193'? 2 Sheets-Sheet 2 u r EQ- L S i K g hm Patented Aug. 2, 1938 UNITEDSTATES PATENT OFFICE CONSTRUCTION OF MAPS FROM PHOTO- GRAPHS TAKEN FROM THE AIR Henry Georges Fourcade, Humansdorp, Cape Province, South Africa Application April 12, 1937, Serial No. 136,481 In Great Britain May 11, 1936 7 Claims. (Cl. 33-20) This invention relates to the construction 'of ner, in a rectifying camera, these rectified posimaps from photographs taken from the air, by tives being then used in the apparatus constructmeans of the coincidences of projected images of ed according to the present invention. But, the photographs, when the tilt of the photographs in the air is The projection of two photographs to combine too small to afl'ect definition seriously at any one 5- stereoscopically on a screen was first effected by projection level, the air photographs may be used dAlmeida in 1858. He used green and red without previous rectification, because, in the lights for projecting the images and red and present apparatus, definition is influenced by tilt green filters for viewing them. only and not by change in height of the projec- 10 The idea of utilizing the method of constructtion distance. In this case the photographs 10" ing maps from the coincidences of the images themselves or the mirrors projecting them may when the photographs and lenses are disposed in be tilted to produce the rectified images directly. the same relative positions as they were in space The invention mainly consists in the combinawhen the photographs were taken is due to tion of a double projecting system for the con- Scheimpfiug. struction of maps with an autofocussing system. 15

The drawback of this method is that it can be The invention also consists in the improved applied strictly only when the country; to be autofocussing system comprising a pivoted mapped lies in a plane. If the lenses and photostraight rule adapted to co-operate with a vergraphs are raised or lowered to bring coincidence tically movable bridge of the apparatus and a of points above or below this plane, the condistance piece connected with a plate carriage vergence of the two images is altered when they horizontally movable on the said bridge, preferare brought again into focus. If the focus is ably through the intermediary of two rollers renot altered, the convergence remains the same, spectively associated with the said bridge and but the images being out of focus become blurred distance piece on the plate carriage.

and precision is lost. This effect is minimized by Another feature of the invention consists in 25 reducing the aperture of the lenses but is still adapting the distance between a lens and its reconsiderable since sufiicient light must be adfleeting mirror in the double projecting system i t to render t p jection visible. The to be varied and the pivot of the autofocussing scale of the projected image is determined by the rule to be correspondingly vertically displaced,

focal length of the lenses and can be varied only in order to compensate for difference in height 30 between small limits. of the air stations.

Various modifications 0f the method have been The invention also consists in the improved ade by Gasser in G y, Nistl'i in Italy, and combined double projecting system for the con- Nelles in Canada, but n al Of h the attempt struction of maps and autofocussing system, as

is made to maintain equa ity of Co ve of hereinafter more particularly described with ref- 35 t e ays in Space and 0f the rays in the D erence to the accompanying drawings, in which:

jection, with the result that every essential de- Figures 1 2 d 3 are explanatory diagrams, fect of the method remains. and

The object of the present invention is to pro- Figure 4 is an elevation of the improved 40 Vide improved means whereby both images paratus, diagrammatically illustrated by way of 40 which may have been taken at difierent heights, examma remain in sharp focus at all projection levels, I will, first of an refer to the principles on while their geometrical relations remain mathewhich the present invention is based and give a maticany accurate at the same Wlde theoretical explanation of its essential features.

range of scales for the constructed map is made Referring to F1 gum 1, let A and B represent 45 available.

a pair of rectified copies, with a common pro- In contradistinction to the methods hitherto jection distance 2,, of air photographs taken at em loyed, in which the photographs are set in pos i tions corresponding to those they occupied helghts b e hb above fl 2; in space, in the present invention these positions Prolectlon dlstaflce 1S equa 0 e P l are first determined with the apparatus itself, or clpal dlstahce 0f e photograph, multiplied else independently by known methods, and t by the ratio between the scale of the rectified knowledge of these positions is utilized to conpy a the 9 of h orlgmal p vert the pictures into their equivalent projections grap h p pal dlstance of the p o oupon a horizontal plane, in a well known mangraph is the length of the perpendicular between 55 the contours :to scale, it is suflicient to raise the the internal perspective centre and the plane of the photograph.

For the reprojection, on a scale s of the points on the datum plane we must have, B being the aerial base, b:Bs

or, if F is the common focal length of the two r i For the projection, on the same scale, of the points on another plane PQ at a height above,

8 0., or, conversely to lower the lens assembly equally by the same amounts, provided the plates A and Bare automatically or otherwise kept in a conjugate focuswith the plane of theprojection.

By means of a hand Wheel actuating, through g-suitable mechanism, the lens system vertically,

the tracing point may be kept in apparent contact with any detail and its plan traced irrespective of variation in height.

Referring to Figure 2 which is a diagram of the apparatus, the plates A and B, the projection lenses and the reflectors are carried on a horizontal bridge which may be moved vertically, by

means of a pair of screws simultaneously actuated by a hand wheel, from the surface plate MN on ;;which the projections are made,.as hereinafter more particularly described with reference to Figure 4. By setting Sa+m=flc and Sb +m=,v1b, the lenses mirrors, and plate centres may be kept at the same height, that is on a single slide of the bridge, the difference between flu and flb which is constant for one pair of plates being taken up,

level of the optical axes and likewise at a horizontal distance F from the lower centre. 'Each autofocussing system is at any arbitrary distance on its side of the apparatus and actuates the plate carriage by means of 'a distance piece In or 1b the length of which remains constant after each setting of a pair of plates," 7

Referring to-Figure 3, AB is the rule pivoted at B and touching a point P of the plate carriage and a point A fixed above the bridge.

being equal to 12, and PQ a constant, the plate will remainin conjugate focus with MN if connected with P by a distance piece of constant' length. We have:

w Referring now'toli'igure which illustrates.

diagrammatically one mode of carrying'the invention into effect, a is a travelling bridge adapted to slide vertically on two pillars b, c are screws in screw threaded engagement with the bridge'member a and connected together through the intermediary of a cross-shaft d-and bevel gears e andadapted to'be simultaneously operated by means of a hand wheel ,1 in order to cause.

the b-ridgemember a to be shifted up or down. This vertical displacement. of the bridge member is indicated on a scaled. j

h are sliding stages carried on the bridge mem ber a and holding the photographs to be pro-v jected. i are the lanterns for illuminating the photographs, k the projection lenses which are of equal focus, and Z are the reflecting mirrors associated with the respective lenses and photographs, the centres of both photographs and both lenses being set in a straight line. I The two reflecting mirrors Z may be separated so as tojbe.

a distance apart equal to the horizontal distance between the two air stations on the scale of the.

map to be drawn, whichidi'stanc'e'is indicated by a scale m provided on the'bridge member. One

7 of the lenses k is carried'on the bridge member a in such a manner that it may be displaced horizontally thereon'and beset'at the desired point along thescale m so as to lie at a distance from its corresponding mirror I, equal to the difference in height of the air stations on the height scale g. The other lens 70 maybefixed relatively to its corresponding'mirror,,or be also so arranged as to be capable of relative displacement with respect to its mirror Z; Referring now to the autofocussing system, th same comprises straight rules p pivoted at q and associated with the slidingplate stages h, each of which is provided with a distance piece 71 carrying a roller 0 which abuts against the straight rule p and. is kept pressed against it by means of acord n tensioned by a counterweight 1L. Of course; instead of such tensioned cord, use may be made of a suitable spring. The straight rule 10 isalso kept in contact with a roller t carried by a bar fixed to the bridge membera; t" is a suitable yielding strap, by means of which'the rule 11 is kept against the roller -t. The pivot q of each autofocussing rulelies at a height above the plane of the board r on which the projection is made equal to twice the focal length of the projection lenses lc, less the distance along the optical axis, between the front nodal point of the lens and its mirror, but one of the pivots is movable vertically in a slide, .and is set by means of a scale s at a height differing from that of the other pivot by an amount equal to the difference in height of the air stations on the height scale a. The rollers t lie permanently fixed at a height above the rollers 0 equal to the focal length of the projecting lenses and at the same distance horizontally from the pivots of the rules 11.

I wish it to be understood that the details of carrying the invention into effect may be modified in various respects without in any way departing from the spirit of the invention.

I claim:

1. An apparatus for the construction of maps from photographs taken from the air, by means of the coincidences of projected images of the photographs, comprising in combination a vertically movable bridge, two projection systems for the construction of maps, both carried by the bridge, and means for simultaneously and automatically keeping the scale of the coinciding parts of the images constant, the images in focus and the displacement of the bridge proportional to the height of the coinciding parts of the images, consisting of a plate carriage displaceable on the bridge, and a pivoted straight rule adapted to cooperate with the bridge and with the plate carriage.

2. An apparatus as claimed in claim 1 and having rollers associated with the bridge and the plate carriage, by means of which the straight rule co-operates with the bridge and the plate carriage.

3. An apparatus as claimed in claim 1, in which each projection system includes a projection lens and a mirror, and in which the pivot of the straight rule lies at the height above the plane of the board on which the projection is made equal to twice the focal length of the projection lenses, less the distance along the optical axis between the front nodal point of the lens and its mirror.

4. An apparatus as claimed in claim 1, in which each projection system includes a projection lens and a mirror, and in which the pivot of the straight rule lies at the height above the plane of the board on which the projection is made equal to twice the focal length of the projection lens, less the distance along the optical axis between the front nodal point of the lens and its mirror, and having a second straight rule pivoted at a variable distance from the plane of the board on which the projection is made, the pivot thereof being vertically displaceable, and capable of being set by means of a scale, at a height differing from that of the other pivot by an amount corresponding to the difference in height of the air stations.

5. An apparatus as claimed in claim 1 and having rollers associated with the bridge and the plate carriage, by means of which the straight rule co-operates with the bridge and the plate carriage, and in which the roller which is associated with the bridge member lies with respect to the other roller associated with the plate carriage at a height above the same, which is equal to the focal length of the projecting lenses, and at the same distance horizontally from the pivot of the rule.

6. An apparatus for the construction of maps from photographs taken from the air, by means of the coincidences of projected images of the photographs, comprising in combination a vertically movable bridge and two projection systems each comprising a plate carriage carried by the bridge and movable on it, an optical system carried by the bridge, a straight rule pivoted to a stationary part of the apparatus, and guides on the bridge and on the plate carrier for the straight rule, for obtaining the focussing movement of the plate carrier corresponding to the vertical displacement of the bridge.

7. An apparatus as claimed in claim 1, in which each projection system includes a projection lens and a mirror and in at least one projection system the lens and mirror are relatively movable.

HENRY GEORGES FOURCADE. 

